Abrasive blasting definitions

An "abrasive" is a solid substance used in an abrasive blasting operation. See the definition in 1910.94(a)(1)(i).

• This term covers materials like sand, grit, shot, or other solids intentionally propelled to clean or finish a surface.
• When planning controls, treat the abrasive as a source of dust and consider its composition and toxicity per 1910.94(a)(2)(i).

An "abrasive-blasting respirator" is a respirator constructed so that it covers the wearer's head, neck, and shoulders to protect from rebounding abrasive. See 1910.94(a)(1)(ii).

• Employers must ensure operators wear appropriate abrasive-blasting respirators when required by 1910.94(a)(5), for example when working inside blast-cleaning rooms or when silica sand is used without physical separation.
• Respirators used must meet NIOSH approval and the employer must implement a respiratory protection program in accordance with 1910.134.

A "blast cleaning room" is a complete enclosure in which blasting is performed and where the operator works inside the room to operate the blasting nozzle and direct the abrasive flow. See 1910.94(a)(1)(iv).

• This differs from an enclosure where the operator stands outside and operates the nozzle through openings; that arrangement is described in the same paragraph as a separate enclosure type and requires different controls to prevent dust escape (see 1910.94(a)(1)).
• When operators are inside a blast-cleaning room they must wear abrasive-blasting respirators as required by 1910.94(a)(5)(ii)(a).

Employers must keep respirable dust or fume concentrations in the operator's and other workers' breathing zones below the limits in [1910.1000]. See 1910.94(a)(2)(ii).

• Measure exposures in the breathing zone and compare them to the permissible exposure limits in 1910.1000.
• Use engineering controls such as enclosures, exhaust ventilation, and dust collectors described in 1910.94(a)(3) and 1910.94(a)(4) before relying on respirators.

Organic abrasives that are combustible must be used only in automatic systems, and where flammable or explosive dust mixtures may be present, equipment and wiring must meet NFPA and OSHA requirements and the blast nozzle must be bonded and grounded. See 1910.94(a)(2)(iii) and the incorporation by reference at 1910.6.

• Follow American National Standard Installation of Blower and Exhaust Systems for Dust, Stock, and Vapor Removal or Conveying, Z33.1-1961 (NFPA 91-1961) as incorporated in 1910.6.
• Bond and ground the blast nozzle to prevent static charge build-up and reduce ignition risk.

Blast-cleaning enclosures must be exhaust ventilated so that a continuous inward flow of air is maintained at all openings during blasting. See 1910.94(a)(3)(i).

• All air inlets and access openings must be baffled or arranged to minimize escape of abrasive or dust and prevent visible spurts of dust (1910.94(a)(3)(i)(a)).
• The exhaust rate must clear dust-laden air promptly after blasting stops (1910.94(a)(3)(i)(b)).

Before opening the enclosure, the blast must be turned off and the exhaust system run long enough to remove the dusty air inside. See 1910.94(a)(3)(i)(c).

• This minimizes worker exposure to respirable dust when access doors are opened.
• Employers should document how long the exhaust must run based on the enclosure size and ventilation capacity, consistent with the requirement that the exhaust rate provide prompt clearance (1910.94(a)(3)(i)(b)).

Observation windows must use safety glass protected by screening where hard deep-cutting abrasives are used. See 1910.94(a)(3)(i)(d).

• Inspect windows regularly to ensure the screens and glazing are intact.
• Replace damaged protective screening or glass to prevent projectiles or abrasive fragments from striking people outside the enclosure.

Slit abrasive-resistant baffles must be installed in multiple sets at small access openings, doors must be flanged and tight when closed, and doors on blast-cleaning rooms must be operable from both inside and outside except for a small operator access door. See 1910.94(a)(3)(i)(e) and its subparts (1910.94(a)(3)(i)(e)(1) and 1910.94(a)(3)(i)(e)(2)).

• Inspect and replace baffles regularly to prevent dust escape.
• Ensure emergency egress is maintained by making doors operable from inside where required.

No — where the abrasive is recirculated, the exhaust ventilation system must not be relied on to remove fines; an abrasive separator is required. See 1910.94(a)(4)(ii).

• Install and maintain a dedicated abrasive separator to remove fines from spent abrasive.
• Relying on the exhaust alone can cause system blockage and reduced performance; check static pressure drop as required by 1910.94(a)(4)(i)(b).

Dust collectors must be set up so accumulated dust can be emptied and removed without contaminating other working areas. See 1910.94(a)(4)(iii).

• Locate dust collector access points and disposal areas to prevent cross-contamination.
• Use sealed containers and local procedures for dust removal to keep other work areas clean and safe.

Respirators used in abrasive-blasting operations must be approved by NIOSH under 42 CFR part 84. See 1910.94(a)(5)(i).

• Employers must select respirators based on the specific dust hazards and ensure the respirator model is NIOSH-approved.
• Implement a respiratory protection program in accordance with 1910.134 as required by 1910.94(a)(5)(iv).

Abrasive-blasting respirators must be worn by all abrasive-blasting operators when working inside blast-cleaning rooms, when silica sand is used in manual blasting without physical separation, or where toxic dust may exceed limits in [1910.1000]; properly fitted particulate-filter respirators may be used only for short, intermittent, or occasional dust exposures. See 1910.94(a)(5)(ii) and 1910.94(a)(5)(iii).

• Dust-filter respirators are allowed for cleanup tasks or unloading where enclosure or engineering controls are not feasible (1910.94(a)(5)(iii)).
• Dust-filter respirators are not allowed for continuous protection when silica sand or toxic materials are used (1910.94(a)(5)(iii)(b)).

Employers must implement a respiratory protection program in accordance with [1910.134] for employees who use respirators required by this section. See 1910.94(a)(5)(iv) and 1910.134.

• The program must include fit testing, medical evaluations, training, and maintenance per 1910.134.
• Ensure supplied air for abrasive-blasting respirators meets quality requirements in 1910.134(i) as referenced in 1910.94(a)(6).

Operators must be equipped with heavy canvas or leather gloves and aprons or equivalent protection, and safety shoes where heavy pieces are handled; eye and face protection must be provided when the respirator does not protect those areas. See 1910.94(a)(5)(v) and related subparts.

• Protective footwear must meet 1910.136(b)(1).
• Eye and face protection must conform to 1910.133 when respirators do not provide this protection.

Air supplied to abrasive-blasting respirators must be free of harmful quantities of dusts, mists, or noxious gases and must meet the supplied-air quality and use requirements in [1910.134(i)]. See 1910.94(a)(6) and 1910.134(i).

• Test and monitor compressor and supply systems to ensure air purity consistent with [1910.134(i)].
• Provide appropriate filtration and safeguards to prevent contamination of breathing air.

Employers must prevent dust accumulation on floors or ledges outside abrasive-blasting enclosures, promptly clean dust spills, and keep aisles and walkways clear of abrasives that could create slipping hazards. See 1910.94(a)(7).

• Regular housekeeping schedules should cover cleanup of steel shot or similar abrasives.
• Use proper tools and PPE during cleanup to avoid re-entrainment of dust into the work area.

Paragraph (a) applies to all operations where an abrasive is forcibly applied to a surface by pneumatic or hydraulic pressure or by centrifugal force; it does not apply to steam blasting, steam cleaning, or hydraulic cleaning methods done without abrasives. See 1910.94(a)(8).

• If you use no abrasives (e.g., steam cleaning without abrasives), this paragraph does not apply.
• When abrasives are used, follow the enclosure, ventilation, PPE, and respiratory protection requirements in paragraph (a).

A "particulate-filter respirator" is an air-purifying respirator that removes most dust or fume from air passing through it, and "respirable dust" is airborne dust small enough to pass through the upper respiratory system to reach lower lung passages. See 1910.94(a)(1)(ix) and 1910.94(a)(1)(x).

• Use particulate-filter respirators only where appropriate per 1910.94(a)(5)(iii), and implement a respiratory program per 1910.134.
• Determine if dust is respirable by particle-size sampling and compare exposures to 1910.1000 limits.

Yes — "Grinding wheels" are all power-driven rotatable wheels (except disc wheels) made of abrasive particles bonded together and used for peripheral grinding. See the definition in 1910.94(b)(1)(viii) for the exact wording.

Polishing and buffing wheels are power-driven rotatable wheels made wholly or partly of textile fabrics, wood, felt, leather, paper (sometimes coated with abrasives) for polishing, buffing, and light grinding; a portable grinder is any power-driven rotatable grinding, polishing, or buffing wheel mounted so it can be manually manipulated. See 1910.94(b)(1)(xiv) and 1910.94(b)(1)(xv) for the precise definitions.

Employers must provide and use a local exhaust ventilation system whenever dry grinding, dry polishing, or buffing is performed and employee exposure (without regard to respirator use) exceeds the permissible exposure limits in 1910.1000 or other applicable PELs. See the requirement in 1910.94(b)(3).

Hoods must be designed, located, and placed so dust and dirt fall or are projected into the hood in the direction of airflow, and wheels or belts must not be run in ways that throw dust into the operator's breathing zone. See the design and placement requirement in 1910.94(b)(3)(i).

OSHA requires the minimum exhaust volumes shown in Table G-4 for grinding wheels on floor stands, pedestals, benches, and special-purpose machines, with a recommended minimum duct velocity of 4,500 feet per minute in the branch ducts and 3,500 feet per minute in the main (header) pipe. See 1910.94(b)(3)(ii) for the table reference and the duct velocity guidance.

Increase the required exhaust volume in direct proportion to the ratio of the new wheel width to the width shown in Table G-4 (i.e., multiply the table volume by new width ÷ table width). For example, OSHA shows the method: if a wheel width is 4½ inches and the table uses 4 inches, calculate 4.5 ÷ 4 × table volume. See the table and example in 1910.94(b)(3)(iii) and Table G-4.

Single-spindle disc grinders must be hooded and connected to branch pipes with exhaust volumes from Table G-6; double-spindle disc grinders need a hood enclosing the grinding chamber with branch pipe volumes from Table G-7; vertical-spindle disc grinders must be encircled with hoods to remove dust. See 1910.94(b)(3)(iv), 1910.94(b)(3)(v), and 1910.94(b)(3)(vi).

When the work is outside the hood, air volumes must be increased as specified in the American Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960 (section 4, exhaust hoods). See the requirement in 1910.94(b)(3)(ix).

Exhaust systems should be designed and tested in accordance with the American Standard Z9.2-1960, and all exhaust systems must have suitable dust collectors. See the design and testing guidance in 1910.94(b)(4)(i) and (ii) and the dust collector requirement in 1910.94(b)(4)(iii).

Hoods must be at least as strong as the structural strength specified in Tables O-1 and O-9 of 1910.215 because hoods serve the dual function of containing wheel bursts and collecting dust. See 1910.94(b)(5)(i)(a).

The adjustable tongue must be kept in working order and adjusted to within one-fourth inch of the wheel periphery at all times. See the requirement in 1910.94(b)(5)(ii).

For portable grinding operations conducted in a partial enclosure, maintain an average face air velocity of not less than 200 feet per minute; for cradle grinding and polishing operations the average face velocity into the enclosure opening must be at least 150 feet per minute, and the operator must be positioned outside the working face. See 1910.94(b)(5)(iv) and 1910.94(b)(5)(vi).

Hoods for horizontal single-spindle disc grinders must leave at least a 1-inch space between the back of the wheel and the hood and have a periphery clearance to permit suction; the side opening must be no larger than required but never smaller than twice the area of the branch outlet. Horizontal double-spindle disc grinders must have an encircling hood with openings no smaller than twice the area of branch outlets. Vertical-spindle disc grinders must be encircled so heavy dust is drawn off the disc surface and lighter dust exhausted through a continuous slot at the hood top. See 1910.94(b)(5)(vii), 1910.94(b)(5)(viii), and 1910.94(b)(5)(ix).

The minimum slot velocity is given by the formula: Minimum slot velocity = 2,000 ft/min minus 1/2-inch slot width (per the figure notes), and the entry loss is calculated as 1.0 slot velocity pressure plus 0.5 branch velocity pressure. See the figure notes and slot guidance in 1910.94(b)(5)(xi) and the related figures in the same section.

A spray booth is a type of enclosure used for spray-finishing operations and the detailed design and equipment requirements for spray booths are set out in 1910.107(a).

• The definition in 1910.94(c)(1)(ii) points you to 1910.107(a) for the full description and requirements.
• Use 1910.107(b) and the succeeding subsections for construction, ventilation, and ignition-source controls that apply to spray booths.

No. Combustible materials must not be used to construct a spray booth or its supply or exhaust ducts; the materials must be noncombustible.

• This prohibition is explicit in 1910.94(c)(3)(i)(b).
• For related electrical and ignition-source requirements, see 1910.94(c)(3)(i)(a) and the spray-booth equipment rules in 1910.107(b)(10).

Overspray filters must be installed in locations that are easily accessible for inspection, cleaning, or replacement.

• This requirement is stated in 1910.94(c)(3)(iii)(a).
• Also follow the installation and maintenance requirements in 1910.107(b)(5), which 1910.94(c)(3)(iii) incorporates by reference.

If the water-chamber enclosure in a wet or water-wash spray booth is made of steel, it must be at least 18 gauge and adequately protected against corrosion.

• This specification appears in 1910.94(c)(3)(iv)(a).
• The regulation also requires chambers to provide adequate scrubbing action via nozzles, headers, or other devices per 1910.94(c)(3)(iv)(b).

Unobstructed walkways inside a spray booth must be at least 6½ feet high and kept clear from the work location to a booth exit or open front; booth exits must meet specific minimum widths depending on exit configuration.

• 1910.94(c)(3)(ii) requires walkways at least 6½ feet high.
• If the open front is the only exit, that exit must be at least 3 feet wide; where multiple exits exist, exits can be at least 2 feet wide provided the maximum distance from work location to an exit is 25 feet or less, as stated in 1910.94(c)(3)(ii).

Doors on spray booth exits must open outward from the booth.

• This requirement is specified in 1910.94(c)(3) and clarified in the accompanying construction text.
• Outward-opening doors help ensure quick egress and reduce the chance of being trapped by internal pressure or obstructions.

If negative pressure exists in inlet ductwork and there is a risk of harmful gases, fumes, or mists infiltrating from areas the duct passes through, all seams and joints must be sealed.

• See 1910.94(c)(5)(ii)(a) for this sealing requirement.
• Proper sealing prevents contaminated air from being drawn into the makeup-air stream supplying the spray booth, improving worker protection.

Inspection or clean-out doors must be provided approximately every 9 to 12 feet of running length for ducts up to 12 inches in diameter, with larger ducts allowed greater spacing as needed.

• 1910.94(c)(5)(iii)(e) sets this guideline and also requires clean-out access for servicing fans and provision of drains where necessary.
• Follow good design practice for larger ducts; the rule allows greater spacing for larger pipe diameters when appropriate.

Exhaust ductwork must be sized using good design practice that considers fan capacity, duct length, number of turns, size variation, and the character of materials being exhausted, and employers are directed to ANSI Z9.2-1960 for further design details.

• This requirement is in 1910.94(c)(5)(iii)(b).
• Use ANSI Z9.2-1960 (incorporated by reference in 1910.6) for supplemental guidance on duct sizing and layout.

Minimum maintained inlet velocities for spray booths must meet the values shown in Table G-10, and these velocities depend on the booth type and operating conditions as specified in 1910.94(c)(6)(i).

• 1910.94(c)(6)(i) requires that inlet velocity be no less than the values listed in Table G-10 for the applicable operating condition.
• The table and its notes (including design vs. compliance ranges and limits on crossdrafts) are part of 1910.94(c)(6).

The total air volume exhausted through a spray booth must be enough to dilute solvent vapor to at least 25 percent of the solvent’s lower explosive limit (LEL).

• This requirement is stated in 1910.94(c)(6)(ii).
• Use the example and formula in the standard (see the worked example using toluene and Table G-11) to calculate cubic feet per minute needed based on gallons of solvent evaporated per minute.

A fan plenum used to equalize or control exhaust air distribution must be strong and rigid enough to withstand the differential air pressure and loads it will experience, and must be constructed to facilitate cleaning, meeting at least the equivalent construction specifications of [1910.94(c)(5)(iii)].

• See 1910.94(c)(5)(i)(a) for the plenum strength and cleanability requirement.
• The referenced construction specifications to which it must be at least equivalent appear in 1910.94(c)(5)(iii), which covers duct support, joints, and clean-out access.

Yes — when an operator works in a booth downstream from the object being sprayed they must wear an air‑supplied respirator (or another respirator suitable for the material) that is approved by NIOSH under 42 CFR part 84. Employers must provide a respirator that matches the hazards of the material being sprayed and that carries the appropriate NIOSH approval.

• The requirement is explicit in 1910.94(c)(6)(iii)(a).
• Make sure the respirator provided is approved for the specific spray material and that employees are trained, fit‑tested, and medically evaluated as required by the employer’s respiratory protection program (see OSHA respiratory protection principles under 29 CFR 1910.134 for program details).

Yes — if a downdraft booth has doors, those doors must be closed while spray painting is taking place. Closing the doors helps ensure the intended airflow pattern and exhaust capture are maintained.

• This requirement is stated in 1910.94(c)(6)(iii)(b).
• Practically, verify doors seal properly and do not interfere with the booth’s exhaust performance; keeping doors open can disrupt airflow and increase worker exposure to overspray and vapors.

Clean, fresh make‑up air equal to the volume of air exhausted from the spray booth must be supplied, and if the make‑up air comes through self‑closing doors, dampers, or louvers those openings must be fully open when spraying and air velocity through them should not exceed 200 feet per minute unless the fan characteristics provide the required booth airflow at higher velocities.

• See the supply requirement in 1910.94(c)(7)(i) and the door/velocity rules in 1910.94(c)(7)(ii).
• Practical tips: size make‑up air fans to match exhaust flow, and ensure self‑closing doors/dampers are interlocked or designed to remain fully open during spraying so you don’t starve the booth of replacement air.

You must design fan static pressure assuming the filters are dirty, install a pressure gauge to show the pressure drop across the filters, mark that gauge with the pressure at which filters need cleaning or replacement, and replace or clean filters whenever the pressure drop becomes excessive or whenever booth face airflow falls below the value in Table G-10.

• These requirements appear in 1910.94(c)(7)(iii)(a) and 1910.94(c)(7)(iii)(b).
• Practical steps: obtain filter performance data from the manufacturer, set the gauge markings to the manufacturer’s recommended pressure drop or the point at which your measured booth airflow drops below Table G-10, and log filter checks so replacements are timely and documented.

No — no means of heating make‑up air shall be located inside a spray booth. If make‑up air is heated elsewhere and combustion products are allowed to mix with the supply air, specific precautions apply: (1) gas must have a distinctive odor to warn workers of leaks, (2) the gas feed rate must be limited so an unburned release would not exceed 200 ppm carbon monoxide or 2,000 ppm total combustible gases, and (3) a fan must move the heated mixture from the plenum to the booth.

• The prohibition on locating heaters in the booth is in 1910.94(c)(7)(iv)(c), and the heating and temperature requirements are in 1910.94(c)(7)(iv)(a)–(b).
• The combustion‑product precautions are set out in 1910.94(c)(7)(iv)(d), 1910.94(c)(7)(iv)(f)(1), 1910.94(c)(7)(iv)(f)(2), and the delivery fan requirement in 1910.94(c)(7)(iv)(f)(3).
• Practical checklist: keep heaters out of the booth; if combustion‑heated make‑up air mixes with supply air, ensure odorant, gas‑supply limits, CO monitoring as needed, and a fan to deliver the conditioned air to the booth.